As the solid state drive (SSD) technologies have matured, SSDs are gradually used to replace conventional hard disk drives (HDDs). Compared to a conventional SSD, the HDD features advantages of a fast response speed in data access, low power consumption and a light weight.
The SSD primarily utilizes a floating gate transistor of a flash memory to store bit data. The number of bits that each transistor can store is categorized into two potential storage modes—a single-level cell (SLC) mode, and a multi-level cell (MLC) mode. When applying the SLC mode, the potential only changes between two voltages. That is, each transistor stores only one bit of data. When applying the MLC mode, each transistor stores two to three bits of data. Thus, when applying the MLC mode, the number of bits of data stored in each transistor is several times of that when applying the SLC mode. Further, flash memories that implement the MLC mode are quite low in cost. However, applications based on the MLC mode have a lower response speed in data access and also a shorter life cycle. In contrast, although flash memories based on the SLC mode are more stable and have a faster response speed in data access and a longer life cycle, they suffer from a lower data storage density and higher production costs.
Therefore, many manufacturers have proposed hybrid SSDs that includes both the SLC potential storage mode and the MLC potential storage mode. For example, the Taiwan Patent No. I385517 discloses a storage device that achieves hybrid storage by using a first flash memory and a second flash memory different from the first flash memory. However, as the above disclosure involves two different types of flash memories, the production costs of the above disclosure remain limited to costs of flash memories based on the SLC potential storage mode and cannot be effectively reduced.